Guard against older Optimizely SDK missing getCampaignStates

Older Optimizely SDK versions don't expose state.getCampaignStates.
Without this guard the call throws at runtime and prevents every
context the plugin would attach, not just the Optimizely one.
Return an empty array instead so the tracker keeps working.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: matus-tomlein

plugins/browser-plugin-optimizely-x/src/index.ts

@@ -76,7 +76,7 @@ export function OptimizelyXPlugin(): BrowserPlugin {
    */
   function getOptimizelyXSummary(): OptimizelyxSummary[] {
     const state = getOptimizelyXData('state');
-    if (state == null) return [];
+    if (state == null || typeof state.getCampaignStates !== 'function') return [];
 
     const campaignStates = state.getCampaignStates({ isActive: true }) || {};
     const visitor = getOptimizelyXData('visitor');